Method for examining the structure of through-holes of a component

ABSTRACT

Methods for examining through holes of a component according to prior art generally use hot gases for the thermographic detection of blockages. The inventive method for examining the structure of through holes of a component considerably simplifies said techniques, using a medium which has at least one absorption edge in the region of the wavelength of the camera and thus appears opaque in the camera image.

CROSS REFERENCE TO RELATED APPLICATION

This application is the US National Stage of International ApplicationNo. PCT/EP2003/010172, filed Sep. 12, 2003 and claims the benefitthereof. The International Application claims the benefits of EuropeanPatent application No. 02024601.3 EP filed Nov. 4, 2002, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method of checking the structure ofthrough-holes of a component according to the precharacterizing clauseof claim 1.

BACKGROUND OF INVENTION

Through-holes of components, for example laser-drilled holes, inparticular cooling-air holes of gas turbine blades, often have complexgeometries that differ from a cylindrical form. The diameter of the holethat is effective for flow, the location of the hole in the wall of thecomponent, the position and the location and the offset of the diffusors(outflow region widened in cross section) of these holes vary on accountof tolerances of the casting, laser or erosion process for example, oron account of the respective production conditions.

The effectiveness of the cooling-air bores on the airfoil profile of theturbine blade results from the complex interrelationship between thesestated variables. Up to the present time, they cannot be determined ormeasured in an automated manner or without great technical expenditure.

With the conventional methods, the continuity of bores is checked by thedetection of the heated component surface, i.e. if the hole is blocked,no heating of the material at the bore hole will occur. The disadvantageof this method is that a small opening (partial closure of the bore)also allows air to pass through and heat up the material. In athermographic image it is scarcely possible to distinguish betweenpartially closed bores and open bores.

Both DE 35 33 186 A1 and DE 197 20 461 A1 show thermographic methods inwhich a heated gas is forced through the cooling-air bores. The supplyof warm air entails considerable expenditure on apparatus. Theconventional thermographic method records the temperature distributionon the component surface which is heated by the warm air. However,conclusions concerning the form of the bore cannot be drawn from theinformation which can be obtained.

SUMMARY OF INVENTION

It is therefore the object of the invention to overcome this problem.

The object is achieved by a method of checking the structure ofthrough-holes of a component according to claim 1.

Further advantageous refinements of the method are listed in thesubclaims.

A visual representation of the flow of gas flares emerging from thethrough-holes with the aid of the camera images produced and imageanalysis provides a wealth of information on the formation and locationof the through-holes and permits both process control and designverification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a device 1 with which the method according to the inventioncan be carried out, and

FIG. 2 shows a camera image taken with the method according to theinvention.

DETAILED DESCRIPTION OF INVENTION

The device 1 according to FIG. 1 comprises, inter alia, a computer 3with a screen, to which a camera 13, for example an infrared camera 13,possibly a source of illumination 28 and further control elements 19 areconnected.

Also connected to the computer 3 for example is a supply of medium 7,which controls the flow of a medium (gas, fluid) into the interior ofthe component 10.

This medium then emerges again from through-holes 25 in the surface 22(FIG. 2) of the component 10, for example at the diffusor that ispresent.

The component 10, or at least a through-hole 25, is irradiated by thesource of irradiation 28. The source of irradiation 28 has a specificwavelength range. The source of irradiation 28 may also be ambientlight. The rays of the source of irradiation 28 impinge on the surface22 of the component 10, where they are reflected and absorbed. Thereflected rays are recorded by the camera 13.

The medium has in the region of the wavelength(s) used by the source ofirradiation 28 at least an absorption line, edge or strip.

Since the medium absorbs the rays of the source of irradiation in theregion of the through-hole 25, the rays of the source of irradiation 28which impinge in the region of the through-hole 25 are consequently atleast attenuated, and do not reach the camera 13, or only in anattenuated form.

The wavelength or wavelength range of the source of irradiation (28) canconsequently be detected by the camera (13).

The surface 22 of the component 10 is for example recorded by aninfrared camera 13.

In order to measure the entire surface 22, the component 10 is forexample arranged on an adjusting unit 16, which is movable, for examplerotatable. Similarly, the component 10 may be fixedly arranged and theinfrared camera 13 is moved in relation to the surface 22 of thecomponent 10. The component 10 and the adjusting unit 16 may also bemovable in all three spatial directions.

According to the invention, the medium, for example a gas, absorbs inthe range of the wavelength(s) of the source of irradiation 28 that areused.

The medium is, for example, carbon dioxide (CO2), which has anabsorption band in the range of the wavelength of 3-5 (m. The source ofirradiation 28 possibly has at least a wavelength in the range of 3-5(m. The camera can detect at least this one wavelength of the source ofirradiation 28.

Consequently, it is possible to distinguish this gas from thesurroundings in the camera image as an opaque matter. The gas CO2 isparticularly well suited, since it has similar fluid-dynamic propertiesto air, which is used for example as the cooling medium.

The evaluation of the camera image at individual through-holes 25 leadsto the concentration distribution or propagation direction of the mediumflowing out from the through-hole 25. Given sequential expulsion of CO2clouds and integration of the concentration values, the determination ofthe amount, and consequently of the through-flow capacity, of therespective bore hole is possible from the concentration distribution.With this information, the production parameters, for example of thelaser and erosion processes, can be optimally adapted for individualthrough-holes 22.

The observation by means of stereo perspective or the variation of theobservation angle of the camera 13 and component 10 makes it possible todetermine the three-dimensional propagation of a flare of medium via thediffusor and the adjacent outer profile region. This results inpossibilities, for example numerical models, for verifying the flowdistribution at the through-hole 22 and diffusor.

After that, the analysis of a gas flare allows further statements to bemade concerning the bore diameter and effects of the geometry of thehole on the outflow behavior—and also the angle of emergence, etc.

The flowing medium may have the same temperature as the component 10;therefore, by contrast with the previously known thermographic methods,it does not have to be heated up.

Similarly, however, it is possible to heat up the medium, if anabsorption band in the wavelength range of the camera 13 that is used isachieved by the heating up.

Warm gas or fluid may also flow through the through-hole 25, in order toinvestigate the outflow behavior of warm gases. For example, gas with atemperature that is greater than room temperature also flows through acooling-air bore of a turbine blade during operation.

Control elements 19 coordinate for example the movement of the camera13, the source of irradiation and the component 10 and also the mediumflow 7 in relation to one another.

FIG. 2 shows a camera image taken with the method according to theinvention.

On the surface 22 of the component with the through-hole 25, the mediumflowing out appears for example as black against the considerablylighter-appearing surface.

The outflow region of the gas after emergence from the through-hole 25also appears for example as black against the surroundings.

1-7. (canceled)
 8. A method of examining the structure of through-holesof a turbine component, comprising: flowing a medium through thethrough-hole; irradiating the component by an irradiation source suchthat the medium has at least an absorption line at one or morewavelengths of the irradiation source; and recording the component by acamera while the medium is flowing through the through-holes and beingirradiated.
 9. The method as claimed in claim 8, wherein the componentis a turbine blade with cooling holes as through-holes.
 10. The methodas claimed in claim 8, wherein gaseous carbon dioxide is used as themedium.
 11. The method as claimed in claim 8, wherein the wavelengthwhich can be detected by the camera includes the wavelength range offrom 3-5 μm.
 12. The method as claimed in claim 8, wherein the medium ischosen such that a camera image in the region of the medium appearsopaque.
 13. The method as claimed in claim 8, wherein an infrared camerais used as the camera.
 14. The method as claimed in claim 8, wherein atleast the wavelength or wavelength range of the source of irradiationcan be detected by the camera.